Transformer The most basic form of transformer is composed of two groups of coils wound with wires, which are combined with each other in an inductive way. When an alternating current (with a known frequency) flows in one coil, an alternating voltage with the same frequency will be induced in the other coil, and the induced voltage depends on the degree of coupling and magnetic cross-linking between the two coils.
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Generally speaking, the coil connected to the AC power supply is called the primary coil; The voltage across this coil is called the primary voltage. The induced voltage in the secondary coil can be larger or smaller than the primary voltage, which is determined by the turns ratio between the primary coil and the secondary coil. Therefore, transformers are divided into step-up transformers and step-down transformers.
Most transformers have a fixed iron core with primary and secondary coils wound around it. Based on the high permeability of iron, most of the magnetic flux is confined in the iron core, so the two groups of coils can obtain a fairly high degree of magnetic coupling. In some transformers, the coil is closely combined with the iron core, and the ratio of primary voltage to secondary voltage is almost the same as the ratio of coil turns. Therefore, the turns ratio of transformer can generally be used as a reference index for step-up or step-down of transformer. Because of this step-up and step-down function, transformer has become one of the important accessories of modern power system. Increasing transmission voltage can make long-distance transmission more economical. As for the step-down transformer, the application of power supply is more diversified. It can be said that without transformers, modern industry can't reach the status quo.
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Transformers are also used in experiments, called test transformers. They can be divided into inflatable, oil-immersed and dry-type test transformers. It is the basic test equipment for AC withstand voltage test in power plants, power supply bureaus and scientific research units. They have passed the standards of the State Bureau of Quality Supervision, and are used for the insulation strength test of various electrical products, electrical components and insulation materials under specified voltage.
operating maintenance
1. Prevent transformer from overload operation: Long-term overload will cause coil heating, gradually aging insulation, short circuit between boxes, short circuit between phases or short circuit to ground and decomposition of oil;
2. Prevent transformer core insulation from aging and damage: aging of core insulation or damage of clamping bolt sleeve will cause a large number of eddy currents in the core, resulting in insulation aging caused by long-term heating of the core;
3. Prevent the insulation from being damaged by maintenance: When the transformer is overhauling the suspension core, attention should be paid to protecting the coil or insulating sleeve, and if any scratch is found, it should be handled in time.
Bicomponent structure
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Transformer components include body (iron core, winding, insulation, lead wire), transformer oil, oil tank, cooling device, pressure regulating device, protective device (moisture absorber, safety airway, gas relay, oil storage tank, temperature measuring device, etc. ) and outlet sleeve.
1, core
Iron core is the main magnetic circuit in transformer. It is usually made of hot-rolled or cold-rolled silicon steel sheets with high silicon content and thickness of 0.35 mm\0.3mm\0.27 mm respectively, and coated with insulating paint.
The iron core is divided into two parts: an iron core column and a cross beam, and a winding is sleeved on the iron core column; The cross member is used to close the magnetic circuit.
There are two basic forms of iron core structure: core type and shell type.
2. Curved
Winding is the circuit part of transformer, which is made of double-wire insulated flat wire or enameled round wire.
Composition of transformer
Transformers usually include:
Two or more coils: input alternating current and output induced current.
A circle of metal core: it couples the mutual magnetic field with the coil.
Transformers generally operate at low frequency, and wires are wound around the iron core to form windings. Although the iron core will cause some energy loss, it will help to confine the magnetic field inside the transformer and improve the efficiency. ? Power transformers are divided into core structure and shell structure according to the structure of core and winding and the number of branches of magnetic flux (three-phase transformers have 3, 4 or 5 branches). Their performances are different.
Transformer core
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Thin steel core
Transformers usually use an iron core made of silicon steel as the main magnetic circuit. This can make the magnetic field in the coil more concentrated and the transformer more compact. The iron core of power transformer must be designed to prevent the magnetic circuit from saturation, and sometimes it is necessary to design some air gaps in the magnetic circuit to reduce saturation. The actual transformer core is made of very thin high-resistance silicon steel sheet. This can reduce the loss and heat generated by each layer of eddy current. There are similarities between power transformer and audio circuit. A typical layered iron core is generally in the shape of letters E and I, which is called "EI transformer". One problem with this kind of iron core is that when power is cut off, residual magnetism will remain in the iron core. When the power is switched on again, the residual magnetism will cause the iron core to temporarily saturate. For some transformers with a capacity of more than several hundred watts, if the current limiting circuit is not used, the inrush current will cause the main fuse to blow. More seriously, for large power transformers, inrush current will cause deformation and damage of the main winding.
solid core
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In high frequency circuits such as switching power supply, ferromagnetic powder cores with high permeability and resistivity are sometimes used. At higher frequencies, it is necessary to use insulating magnetic materials, and there are various ceramic materials called ferrite. In some FM radio circuits, some transformer cores use adjustable cores and coupling circuits to realize resonance.
hollow
Coil core
Coil coil is composed of electromagnetic wire, which is used to surround the iron core, generate magnetic field by energizing, or generate induced current by magnetic field.
insulation protection
shielded
Coolant Some transformers use the circulation of liquid substances to dissipate heat. Transformer oil is often used as liquid substance, and its main components are alkanes, cycloalkanes, aromatic hydrocarbons and other compounds. Transformer oil has large specific heat capacity, absorbs heat, expands and rises in volume, forms circulation in the pipeline, and then dissipates heat into the air through the heat dissipation device. Some transformers use gaseous substances (such as sulfur hexafluoride) as coolant. Due to the limitation of thermal conductivity, gas coolant is generally used in small capacity transformers.
As for transformer oil, most of them use mineral oil, and very few transformers use vegetable oil. Mineral oil leakage may pollute the environment, while vegetable oil pollution will be much less. The flash point of vegetable oil is higher than that of mineral oil. Therefore, in the future, vegetable oil may replace mineral oil.
3 production process
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yield
With the sustained, healthy and high-speed development of China's economy, the demand for electricity keeps growing rapidly. 20 1 1 year, the electricity consumption of the whole society is 4.69 trillion kwh, an increase of 1 1.7% over the previous year, and the consumer demand is still strong. The per capita electricity consumption was 3,483 kWh, an increase of 35 1 kWh over the previous year, exceeding the world average.
The rapid development of electric power construction in China has promoted the development of transformer manufacturing in China. 20 1 1 year, the national transformer output reached143 billion KVA, with a year-on-year increase of 6.86%. 20 1 1 China transformer manufacturing enterprises above designated size 146 1 home (main business income is more than 20 million yuan); It achieved sales of 29,065.438+0.40 billion yuan, total profit of 65.438+0.608 billion yuan, asset scale of 263.840 billion yuan, and product sales profit of 33.972 billion yuan.
Transformer The competition in China transformer industry is fierce. Foreign multinational companies have seized a lot of market share, and the number of domestic transformer manufacturers is also growing rapidly. For example, in Yongcheng, Shandong Province, the low-end transformer market is highly competitive. There are more than 20 enterprises with 220KV transformer production capacity and 1 10KV transformer production capacity. However, enterprises that produce transformers above 500KV level have built high barriers to entry through technology and production capacity, and the market structure tends to be stable.
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According to the plan, State Grid will invest about 2.55 trillion yuan in power grid construction during the Twelfth Five-Year Plan period, which is 68% higher than10.5 trillion yuan during the Eleventh Five-Year Plan period. In terms of breakdown, of the 2.55 trillion yuan, 500 billion yuan is used for investment in UHV power grid, 500 billion yuan for investment in distribution network, and 1.55 trillion yuan is used for investment in power grid lines of other voltage levels.
In the investment of UHV power grid, the investment of UHV air conditioner is about 270 billion yuan. The main equipment of UHV AC includes UHV transformer, reactor, GIS combination switch, transformer and other equipment. In UHV investment, equipment investment accounts for about 45%, of which transformers (including reactors) account for about 30%. It is estimated that the market capacity of transformers (including reactors) will exceed 36 billion yuan during the Twelfth Five-Year Plan period.
Winding material
If you want to win a transformer, you must have a certain understanding of the materials related to the transformer, so I will introduce this knowledge here.
1, iron core material
The iron core material for transformer is iron sheet. Adding silicon can reduce the conductivity of steel plate and increase the resistivity. It can reduce the eddy current and its loss. We usually call the steel plate with silicon as silicon steel sheet, which has a great relationship with the quality of silicon steel sheet used in transformer. The quality of silicon steel sheet is usually expressed by magnetic flux density B. Generally, the B value of black iron sheet is 6000-8000, low silicon steel sheet is 9000- 1 1000, and high silicon steel sheet is 12000-65430.
2. Materials commonly used in winding transformer
Enamelled wire, yarn, silk paper wire, the most commonly used enameled wire. The requirements for wires are good electrical conductivity, sufficient heat resistance of insulating paint layer and certain corrosion resistance. In general, it is best to use high-strength polyester enamelled wire of QZ model.
3. Insulation materials
In winding transformer, insulation materials should be used for insulation between layers of bobbin and windings. General transformer frame materials can be phenolic cardboard, epoxy board or cardboard. The interlayer can be isolated by polyester film, telephone paper and 6520 composite paper, and the winding can be isolated by yellow wax cloth or imine film.
4. Impregnating materials
After the transformer is wound, it has to go through the last process, that is, impregnating with insulating paint, which can enhance the mechanical strength of the transformer, improve the insulation performance and prolong the service life. In general, cresol varnish can be used as impregnating material or 1032 insulating paint or resin paint.
4 working principle
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Transformer A transformer is a device that transforms AC voltage, AC current and impedance. When alternating current passes through the primary winding of Shanghai Shuogong transformer, alternating magnetic flux is generated in the iron core (or magnetic core) and voltage (or current) is induced in the secondary winding.
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A transformer consists of an iron core (or magnetic core) and a coil. The coil has two or more windings, of which the winding connected to the power supply is called the primary coil and the rest is called the secondary coil.
Five main categories
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The classification of commonly used transformers can be summarized as follows:
1, according to the number of phases:
1) Single-phase transformer: used for single-phase loads and three-phase transformer banks.
2) Three-phase transformer: used for step-up and step-down of three-phase system.
2, according to the cooling mode:
1) dry-type transformer: it relies on air convection for natural cooling or fan cooling, and is mostly used in high-rise buildings, high-speed toll stations, local lighting, electronic circuits and other small-capacity transformers.
Transformer 2) Oil-immersed transformer: oil is used as cooling medium, such as oil-immersed self-cooling, oil-immersed air cooling, oil-immersed cooling and forced oil circulation.
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3. According to the purpose:
1) power transformer: used to step up and down the voltage of power transmission and distribution system.
2) Transformer: such as voltage transformer, current transformer, measuring instrument, relay protection device, etc.
3) Test transformer: it can generate high voltage and conduct high voltage test on electrical equipment.
4) Special transformers: such as electric furnace transformers, rectifier transformers, voltage regulating transformers, capacitor transformers, phase-shifting transformers, etc.
4, according to the winding form:
1) Double winding transformer: used to connect two voltage levels in the power system.
2) Three-winding transformer: generally used in regional substations of power systems, connecting three voltage levels.
3) Autotransformer: used to connect power systems with different voltages. It can also be used as a common step-up or step-down transformer.
5, according to the core form:
1) core transformer: high-voltage power transformer.
2) Amorphous alloy transformer: Amorphous alloy iron core transformer is a new type of magnetic conductive material, and the no-load current decreases by about 80%. It is an ideal distribution transformer with energy-saving effect, especially suitable for rural power grid and developing areas with low load rate.
3) Shell transformers: special transformers for high current, such as electric furnace transformers and welding transformers; Or power transformers for electronic instruments, televisions, radios, etc.
6 related functions
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The main functions of transformer are: voltage conversion; Current transformation, impedance transformation; Isolation; Voltage stabilization (magnetic saturation transformer); Autotransformer; High-voltage transformer (dry type and oil-immersed type), etc. The commonly used cores of transformers are generally E-type and C-type cores, Xed-type and ED-type CD-type cores.
The most basic type of transformer consists of two groups of coils wound with wires, which are combined with each other in an inductive way. When an alternating current (with a known frequency) flows in one coil, an alternating voltage with the same frequency will be induced in the other coil, and the induced voltage depends on the degree of coupling and magnetic cross-linking between the two coils.
Transformer generally refers to the coil connected with AC power supply, which is called "primary coil"; The voltage across this coil is called the primary voltage. The induced voltage in the secondary coil may be larger or smaller than the primary voltage, which is determined by the "turns ratio" between the primary coil and the secondary coil. Therefore, transformers are divided into step-up transformers and step-down transformers.
Please click to enter a picture description.
Most transformers have a fixed iron core with primary and secondary coils wound around it. Based on the high permeability of iron, most of the magnetic flux is confined in the iron core, so the two groups of coils can obtain a fairly high degree of magnetic coupling. In some transformers, the coil is closely combined with the iron core, and the ratio of primary voltage to secondary voltage is almost the same as the ratio of coil turns. Therefore, the turns ratio of transformer can generally be used as a reference index for step-up or step-down of transformer. Because of this step-up and step-down function, transformer has become one of the important accessories of modern power system. Increasing transmission voltage can make long-distance transmission more economical. As for the step-down transformer, the application of power supply is more diversified. We can say that without transformers, modern industry would not have reached the present situation.